Since an organic EL device employing organic materials has been expected as an application for a display device based on a solid light emission having a popular price and a large viewing surface, substantial development have been conducted.
An organic EL device is constructed generally from a light emitting layer and a pair of counter electrodes which sandwiches the layer. A light emission is a phenomenon as follows; when an electric field is applied between the electrodes, electrons are injected from the cathode side and holes are injected from the anode side. Further, the electrons recombine with the holes in the light emitting layer to produce its excitation state, and the energy from the excitation state is released as a light on returning to the ground state. The conventional organic EL devices required a higher driving voltage and had lower luminance and current efficiency in comparison with inorganic light emission diodes. In addition, the devices have not yet been put to practical use due to notable deterioration of properties thereof.
Although current organic EL devices have been improved by inches, longer lifetime as well as higher current efficiency has been desired. For example, the technology employed the individual mono-anthracene compounds as an organic light emission material has been disclosed (Patent literature 1). However, it has provided with the organic EL devices having for example, only the luminance of 1650 cd/m2 at the luminance of 165 mA/cm2, and also the current efficiency is extremely low so as to put them in practical use.
Further, the technology employing the individual bisanthracene compounds as an organic light emission material has been disclosed (Patent literature 2). However, it has provided with an organic EL device having the low current efficiency such as 1 to 3 cd/A, therefore further improvement has been required so as to put in practical use.
Meanwhile, the organic EL device with a long lifetime, which employed the distyryl compound added by styryl amine or so forth as an organic light emitting material, has been proposed (Patent literature). However, the device has been required to improve its inadequate lifetime further. In addition, the technology employing the organic light emitting medium layer of the monoanthracene compounds or the bisanthracene compounds, and the distyryl compounds has been disclosed (Patent literature 4). However, it has provided with worsened color purity since the emission spectrum become long wavelength due to the conjugated structure of the styryl compounds.
Further, the devices emitting blue light employed the diaminochrysene derivatives have been disclosed in Patent literature 5. However, the device has been required to improve its inadequate lifetime in spite of its excellent current efficiency.
Patent literature 1: Japanese Patent Application Laid-open No. Heisei 11 (1999)-3782, Patent literature 2: Japanese Patent Application Laid-open No. Heisei 8 (1996)-12600, Patent literature 3: International PCT publication No. WO 094/006157, Patent literature 4: Japanese Patent Application Laid-open No. 2001-284050, Patent literature 5: International PCT publication No. WO 04/044088.